1. Field of the Invention
The present invention relates to a volume data transmission system for efficiently transmitting volume data having a 3-dimensional structure consisting of a large number of so-called voxel data.
2. Description of the Related Art
Recently, in an imaging system such as a computed tomography (CT) system capable of obtaining tomographic image information of a specific slice of an object, 3-dimensional image information is obtained by obtaining not only 2-dimensional tomographic image information of a slice but also tomographic image information of a plurality of adjacent slices. The 3-dimensional image information consists of volume data consisting of a group of a large number of so-called voxel data which are obtained by performing arbitrary processing including interpolation processing if necessary for tomographic image data of a plurality of adjacent slices. The tomographic image data of each slice consists of a group of a large number of pixel data. The volume data is used to perform predetermined 3-dimensional image processing, thereby displaying a tomographic image of an arbitrary section intersecting to a region constituted by the volume data, displaying a pseudo 3-dimensional image, which is a perspective image obtained when an object is viewed from various viewing points, on a 3-dimensional space on the basis of the volume data, or displaying a stereoscopic image by so-called stereoscopy.
In some conventional CT apparatuses, the pseudo volume image is displayed as follows. That is, in such systems, the volume data is constituted by voxel data consisting of gradation values (CT values) in units of voxels. These voxel data are binarized in accordance with whether they exceed a predetermined threshold level or fall within the range of a predetermined level. For example, if an object is a human body, a level between a bone and any other portion is used as a threshold for binarization. Then, gray scale gradation is given to a perspective image of the bone viewed from a virtual viewing direction arbitrarily set in a 3-dimensional space, thereby forming and displaying a stereoscopic pseudo 3-dimensional image.
In the system capable of performing image processing as described above, the volume data must be transmitted between sections constituting the system. However, since the volume data is generally constituted by a large amount of data, data transmission for performing the image processing is performed through a high-speed transmission bus in the conventional CT apparatus. A low-speed bus is not used to process the volume data because a transmission time is prolonged when a large amount of data are to be transmitted.
In a system including the above conventional CT system which can process the volume data and display a pseudo 3-dimensional image and a work station (WS), connected through a public communication line such as a telephone line or another communication line, data must be transmitted between the CT apparatus and the WS in order to display a pseudo 3-dimensional image on the basis of the volume data. In this case, the following three types of data transmission can be performed.
(a) CT slice data consisting of gray scale value data is transmitted. (Therefore, in order to transmit volume data, a large number of CT slice data or gray scale voxel data based on the CT slice data are transmitted.)
(b) Binary voxel data which is obtained by binarization is transmitted as preprocessing for forming a pseudo 3-dimensional image.
(c) Pseudo 3-dimensional image data converted from volume data is transmitted.
Processing times and evaluations of the above three methods are as follows.
(1) In method (a), assuming that one pixel consists of 16 bits and 32 image data each having 512.times.512 pixels are differentially compressed (compression ratio =70%) and transmitted at a communication rate of 9600 bps, the processing time is 512.times.512.times.32.times.16.times.70%/9600 bps=2 hours and 43 minutes.
(2) In method (b), when the data as described above are subjected to 3-dimensional processing and binarization, 256.times.256 voxels in each of which 1 pixel =1 bit can be obtained. Therefore, the processing time is 256.times.256.times.256/9600 bps=29 minutes.
(3) In method (c), since an image is transmitted every time a viewing point is changed, the processing time is 512.times.512.times.16.times.70%/9600 bps=5 minutes and 5 seconds. For this reason, the processing is stopped for a very long time every time a viewing point for displaying a 3-dimensional image is changed.
As described above, in any of the above methods, a data transmission time for displaying a 3-dimensional image based on the volume data is prolonged.